The overall objective of this research is to better understand the contribution of somatic cell mutagenesis to the etiology of cancer. We propose to study the molecular mechanisms of somatic cell mutagenesis by characterizing the frequencies and spectra of DNA sequence changes arising in different tissues in transgenic mice. A major goal of this project is to establish a system for studying mutagenesis in animals. Our approach is to study mutations in recombinant vectors inserted into the genomic DNA of transgenic mice. These vectors will be "rescued" from untreated and carcinogen-treated animals, and the mutations will be scored and sequenced following selection in E. coli. The frequencies and spectra of spontaneous mutations will first be determined in vectors rescued from untreated mice. Emphasis will be placed on comparing the relative rates of spontaneous mutagenesis in the major target tissues for carcinogenesis (liver, skin, lung, spleen, kidney and brain). These studies will provide a data base for comparisons with chemically-induced mutations and will assess the genetic fidelity of the techniques used in the production of transgenic animals. Finally, the mutagenicities of the hepatocarcinogenic alkylating agents, dimethylnitrosamine (DMN) and diethynitrosamine (DEN), will be examined. Comparisons of mutation frequencies and spectra in tissues with different carcinogen susceptibilities will help to identify carcinogenic DNA lesions and to determine if organotropism in carcinogenesis correlates with tissue-specific mutagenesis.